Plasma processing apparatus having high frequency power source with sag compensation function and plasma processing method

ABSTRACT

The plasma processing apparatus wherein the means for applying a high frequency voltage, which becomes a voltage waveform in which a positive constant voltage and a negative constant voltage alternate with each other at given cycles, is constituted by a DC power source and a switching circuit (a chopper circuit).

CROSS REFERENCE TO RELATED APPLICATION

This is a divisional of U.S. application Ser. No. 10/795,353, filed Mar.9, 2004. This application relates to and claims priority from JapanesePatent Application No. 2003-357828, filed on Oct. 17, 2003. The entiretyof the contents and subject matter of all of the above is incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a plasma processing apparatus and, moreparticularly, to a plasma processing apparatus which is suitable foretching a workpiece, such as a semiconductor element substrate, by usingplasma and applying a high frequency voltage to the substrate.

2. Description of the Related Art

In conventional plasma processing apparatus, for example, as describedin Patent Document 1, a high frequency voltage having a sine waveformwas applied to an electrode on which a wafer, which is the object to beprocessed, is placed. In this case, as shown in FIG. 12, the ion energydistribution on the wafer has a saddle peak distribution which has twopeaks, one on the high energy side and one on the low energy side.Although ions of the high energy peak contribute to etching, ions of thelow energy peak scarcely contribute to etching. In a case where a highfrequency voltage having a sine waveform is applied, the ratio of thehigh energy peak height to the low energy peak height is almost 1:1.Even when the high frequency voltage is changed, this high/low energyion ratio scarcely changes, posing the problem that the etchingefficiency is low.

Patent Document 1: Japanese Patent Laid-Open No. 5-174995

The object of the present invention is to provide a plasma processingapparatus capable of high etching rate and high performance etching.

BRIEF SUMMARY OF THE INVENTION

In order to achieve the above object, the present invention provides ahigh frequency application means which ensures that a high frequencyvoltage waveform generated in an object to be processed becomesrectangular. Via a high frequency voltage waveform control circuit (asag correction circuit) which changes with time an absolute value ofvoltage on at least either of the positive side and negative side of arectangular high frequency voltage, a high frequency power source whichgenerates a rectangle wave is connected to an electrode on which anobject to be processed is placed. The high frequency voltage waveformcontrol circuit (the sag correction circuit) is automatically controlledwith respect to a monitored quantity so that a rectangular wave isapplied to the object to be processed. As a result, a rectangular highfrequency voltage is applied to the object to be processed. Ionsincident on the wafer, which is the object to be processed, areaccelerated by an electric field in an ion sheath formed on the wafer.This electric field in an ion sheath has a bearing on a potentialdifference between the plasma potential on the ion sheath and the waferpotential and the thickness of the ion sheath. When a rectangular highfrequency voltage is applied to the wafer, low energy ions becomeincident on the wafer during the period of application of a positivevoltage, and high energy ions become incident on the wafer during theperiod of application of a negative voltage. Therefore, by varying theduty ratio of a rectangular high frequency voltage, it is possible tovary the ratio of high energy ions and low energy ions which becomeincident on the wafer. As a result, it becomes possible to perform highetching rate and high performance etching.

According to the present invention, by applying, to a wafer chuckingelectrode 9, a voltage waveform in which an absolute value of highfrequency voltage increases with time and switching between a positivevoltage and a negative voltage occurs, a rectangular high frequencyvoltage is caused to be generated in the wafer 10, and as a result,etching with high efficiency and high performance becomes possible,providing the advantage that the etching selectivity of materials isimproved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross-sectional view of a magnetic field UHFetching apparatus, which is an embodiment of a plasma processingapparatus of the present invention;

FIG. 2 is an explanatory diagram of a circuit configuration of animpedance matching network 11 connected to a wafer chucking electrode 9,a high frequency voltage waveform control circuit (a sag correctioncircuit) 12 and a DC power source 14 according to an embodiment of thepresent invention;

FIG. 3 is a diagram of a high frequency voltage waveform applied to awafer chucking electrode 9 according to an embodiment of the presentinvention;

FIG. 4 is a diagram of a high frequency voltage waveform in a wafer 10according to an embodiment of the present invention;

FIG. 5 is an energy distribution diagram of ions incident on a wafer ina case where the duty ratio of a rectangular high frequency voltage isvaried according to an embodiment of the present invention;

FIG. 6 is a diagram of a rectangular high frequency voltage waveformapplied to a wafer chucking electrode 9 in a comparative example;

FIG. 7 is a diagram of a high frequency voltage waveform in a wafer 10in a case where a rectangular high frequency voltage is applied to awafer chucking electrode 9 in a comparative example;

FIG. 8 is an explanatory diagram of the definition of the amount of sagof a rectangular wave according to an embodiment of the presentinvention;

FIG. 9 is a graph showing the relationship between the ratio of amountof sag and the UHF output in a voltage waveform of a wafer 10 accordingto an embodiment of the present invention;

FIG. 10 is a graph showing the relationship between the ratio of amountof sag and the capacitance of a capacitor in a voltage waveform of awafer 10 according to an embodiment of the present invention;

FIG. 11 is a diagram of a voltage waveform in a wafer 10 in a case wherethe duty ratio T₁/T of a rectangular wave is increased to 50% or greateraccording to an embodiment of the present invention;

FIG. 12 is an explanatory diagram of the energy distribution of ionsincident on a wafer in a case where a high frequency voltage with a sinewaveform is applied to an electrode on which a wafer is to be placed ina conventional method;

FIG. 13 is a longitudinal cross-sectional view of a magnetic field UHFetching apparatus, which is an embodiment of a plasma processingapparatus of the present invention;

FIG. 14 is a longitudinal cross-sectional view of a magnetic field UHFetching apparatus, which is an embodiment of a plasma processingapparatus of the present invention;

FIG. 15 shows a wafer voltage waveform of a wafer 10 obtained bysag-correction and clipping a sine wave voltage waveform and an energydistribution diagram of ions incident on a wafer 10 in each wafervoltage waveform;

FIG. 16 is a diagram explaining the high energy ion ratio in anembodiment of the present invention;

FIG. 17 is a diagram showing the Vpp dependence of the high energy peakratio in an embodiment of the present invention;

FIG. 18 shows a wafer voltage waveform of a wafer 10 obtained bycontrolling the ratio of amount of sag in a sine wave voltage waveformand an energy distribution diagram of ions incident on a wafer 10 ineach wafer voltage waveform; and

FIG. 19 is a diagram showing the dependence of the high energy peakratio on the ratio of amount of sag according to an embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The first embodiment of the present invention will be described withreference to FIG. 1 to FIG. 12.

Embodiment 1

FIG. 1 shows a magnetic field UHF etching apparatus, which is anembodiment of a plasma processing apparatus of the present invention.After depressurizing the interior of a processing chamber 1 defined by ablock 1 a, a discharge tube 1 b and a quartz window 2 via a vacuumsystem (not shown), an etching gas is supplied to the interior of theprocessing chamber 1 via a gas supply device (not shown) and thepressure of the processing chamber 1 is adjusted to a desired processcondition. The processing chamber 1 is located within a magnetic fieldregion generated by a coil 3 and a yoke 4. A UHF wave, which isgenerated by a high frequency power source 5 and has a frequency of 450MHz in this example, travels through an impedance matching network 6,propagates through a coaxial wave guide (cable) 7, passes through thequartz window 2 from an antenna 8, and enters the interior of theprocessing chamber 1. Due to an interaction with the magnetic field, theUHF wave generates plasmas within the processing chamber 1. A wafer 10placed on a wafer chucking electrode 9 is subjected to etching treatmentby the plasmas generated by this UHF wave. In order to control theetching shape of the wafer 10, a rectangular high frequency power source13 is connected to the wafer chucking electrode 9 via a matching device11 and a high frequency voltage waveform control circuit (a sagcorrection circuit) 12, thereby making it possible to apply a highfrequency voltage. An electrode current monitor 15 is connected to ahigh frequency voltage application portion of the wafer chuckingelectrode for measuring a current waveform generated in the electrode. Ameasured electrode current is used as a control signal of the highfrequency voltage waveform control circuit (sag correction circuit) 12.

A DC power source 14 is connected to the wafer chucking electrode 9, thesurface of the electrode being covered with a dielectric film (notshown). As a result, the wafer 10 is chucked by electrostatic force onthe electrode via dielectric film. A shower plate 2 a made of quartz isprovided under the quartz window 2. The etching gas flows between thequartz window 2 and the shower plate 2 a and is introduced into theprocessing chamber 1 through a gas introduction port provided in thecenter of the shower plate 2 a. Because the etching gas is supplieddirectly above the wafer 10, a highly uniform etching is possible. Inthe interior of the processing chamber 1, a quartz cover is provided inorder to prevent pollution.

FIG. 2 shows an example of a circuit configuration of the impedancematching network 11 connected to the wafer chucking electrode 9, thehigh frequency voltage wave form control circuit (sag correctioncircuit) 12 and the DC power source 14. The impedance matching network11, which is constituted by an inductor and a capacitor, requiresfrequency characteristics of a wide band to keep the rectangular voltagewaveform input from a rectangular high frequency power source 13. Theimpedance converter uses a high frequency transformer, for example. Thehigh frequency voltage waveform control circuit (sag correction circuit)12 is composed of a semiconductor element, such as a diode and an FET,and a capacitor. Basically, the high frequency voltage waveform controlcircuit (sag correction circuit) 12 can clip the rf voltage waveforms atany voltage. The high frequency voltage waveform control circuit (sagcorrection circuit) 12 contains diodes D1, D2 and variable capacitancecapacitors VC1, VC2 connected in series thereto. The high frequencyvoltage waveform control circuit (sag correction circuit) 12 ensuresthat a change occurs from a waveform which is clipped flat by thecapacitance of the capacitors VC1, VC2 to a waveform in which anabsolute value of voltage increases with time. The high frequencyvoltage waveform control circuit (sag correction circuit) 12 is notlimited to the circuit shown in FIG. 2, and any circuit can be used ifit can clip a waveform in such a method that an absolute value of highfrequency voltage increases with time, for example, like an integralcircuit or a phase control circuit. Furthermore, an automatic controlcircuit 16, which can vary the capacitance of the capacitors accordingto a monitored quantity, is connected to VC1, VC2. Although in FIG. 1, amonitored quantity is a current obtained from the electrode currentmonitor 15 installed on the electrode, the monitored quantity can be setto anyone of a voltage generated in the object to be processed, acurrent which flows into the object to be processed, a voltage of thewafer chucking electrode, a power applied to the object to be processedand an output power of the high frequency power source. In FIG. 2, VC1and VC2 are controlled so that the waveform of the electrode currentbecomes closest to a rectangular wave. The high frequency voltage whosewaveform has been clipped is applied to the wafer chucking electrode 9via capacitor C2 which blocks a DC current. The DC power source 14 isconnected to the wafer chucking electrode 9 via an inductor L3. Thisinductor L3 prevents the DC power source from high frequency voltage.

FIG. 3 shows a high frequency voltage waveform applied to the waferchucking electrode 9, and FIG. 4 shows a high frequency voltage waveformin the wafer 10. In this case, a frequency of the high frequency voltageis 400 kHz. FIG. 5 shows the energy distribution of ions incident on awafer in a case where the duty ratio of a rectangular high frequencyvoltage is varied. In this case, as shown in FIG. 4, T₁/T is defined asduty ratio wherein T₁ is positive voltage and T is a period in the highfrequency voltage waveform. When the duty ratio is 50%, as with the caseof FIG. 10 where a sine wave high frequency voltage is applied, theratio of ions on the high energy side peak height to ions on the lowenergy side peak height is almost 1:1. However, when the duty ratio isreduced, the proportion of ions on the high energy side increases andwhen inversely the duty ratio is increased, the proportion of ions onthe low energy side increases. If the energy of ions increases, thereaction efficiency of etching (the chemical sputtering ratio) increasesin proportion. Therefore, the larger the amount of ions on the highenergy side, the higher the etching rate. In other words, because theion energy distribution is made monochromatic, it is possible to performprocessing, with the etching shape being vertical and with highaccuracy. For example, vertical shape and high performance working ingate etching is possible. Furthermore, because the relationship betweenion energy and the chemical sputtering ratio differs depending on theobject to be etched, by selecting optimum ion energy, it is possible toimprove the selective etching ratio of a plurality of objects to beetched. For example, it is possible to improve the etching selectivityratio of a hard mask in the etching of a low dielectric constant (Low-k)insulating film and the selective etching ratio with respect to anultrathin oxide film of the substrate in gate etching. In the etching ofa low dielectric constant (Low-k) insulating film, the frequency of thehigh frequency power source was set to 800 KHz.

In a case where a rectangular high frequency voltage as shown in FIG. 6is applied to the wafer chucking electrode 9, the high frequency voltagein the wafer 10 has a waveform as shown in FIG. 7. That is, the absolutevalue of high frequency voltage decreases with time (this phenomenon ishereinafter called a sag). The sag is defined as shown in FIG. 8. Whenthe amplitude of a rectangular wave voltage waveform is denoted by V_(o)(V) and the amount of sag by V_(s) (V), sag ratio (%) is defined by thefollowing equation: $\begin{matrix}{\left\lbrack {{Formula}\quad 1} \right\rbrack{{{Sag}\quad{ratio}\quad(\%)} = {\frac{V_{s}}{V_{o}} \times 100}}} & (1)\end{matrix}$

FIG. 9 shows the UHF power dependence of the ratio on the amount of sag.When the plasma density increases by increasing the UHF power, the sagratio increases. FIG. 10 shows the dependence of sag ratio on thecapacitance of a capacitor formed by a dielectric film for anelectrostatic chuck etc. When the capacitance of a capacitor isincreased, sag ratio decreases. From the foregoing, it can be said thatan effective differentiation circuit, which is formed by the capacitanceof a capacitor of a dielectric film for an electrostatic chuck etc.provided on the surface of the wafer chucking electrode 9 and the plasmaresistance of formed bulk plasmas, is the cause of the sag. When theresistance is denoted by R and the capacitor is denoted by C, the sagV_(s) in a differentiation circuit is generally given by the followingequation:

[Formula 2]V _(s) =V _(o) −V _(o)×exp(−Δt/RC)  (2)

FIG. 11 shows the result of a calculation of the dependence of the ratioof the amount of sag on the capacitance of a condenser when the plasmaresistance is constant. When the high frequency voltage in the wafer 10has a waveform with a high ratio of the amount of sag as shown in FIG.7, the ion energy distribution is a broad one in which the energy widthat a high energy peak and a low energy peak increases and the quantityof ions at the peaks decreases. For this reason, the etching rate, theworking accuracy and the selective etching ratio of materials decrease.In order to perform what is called a sag correction in which an absolutevalue of such a high frequency voltage decreases with time, it isnecessary to perform waveform clipping so that an absolute value of ahigh frequency voltage increases with time due to the action of the highfrequency voltage waveform control circuit (sag correction circuit) 12and to apply a high frequency voltage to the wafer chucking electrode 9.Because the plasma resistance differs depending on etching conditions,the amount of sag also differs. In order to generate a rectangular highfrequency voltage in the wafer 10 as shown in FIG. 4, it is necessary toautomatically control the high frequency voltage waveform controlcircuit (the sag correction circuit) 12. In the present method, the highfrequency voltage waveform control circuit (the sag correction circuit)12 is automatically controlled by using a parameter correlated to theamount of sag occurring in the wafer as a monitored quantity. The highfrequency voltage waveform control circuit (the sag correction circuit)12 may also be automatically controlled by using a computed value of amonitored quantity.

As described above, by applying, to a wafer chucking electrode 9, avoltage waveform in which an absolute value of high frequency voltageincreases with time and switching between a positive voltage and anegative voltage occurs, a rectangular high frequency voltage is causedto be generated in the wafer 10, with the result that high efficiencyand high performance etching becomes possible, providing the advantagethat the selectivity etching ratio of materials is improved.

FIG. 11 shows a voltage waveform in the wafer 10 when the duty ratioT₁/T of a rectangular waveform is increased to 50% or greater. Thehigher the duty ratio is, the higher an absolute value Vdc of the DCvoltage component of a high frequency voltage becomes. That is, apositive voltage decreases. In general, a plasma potential is a positivevoltage, and the plasma potential when the voltage in the wafer 10 is apositive voltage, is approximately 20 V above the potential of the wafer10, whereas the plasma potential at a negative voltage is about 20V.Since the processing chamber 1 is grounded, an ion sheath is formed nearthe inner surface of the processing chamber 1 and a high frequencyvoltage corresponding to the plasma potential is applied to the ionsheath. Since ions accelerated by the electrical field of this ionsheath sputter the wall surface of the inner processing chamber, thewafer 10 is polluted with metal, posing the problem that the electricalproperties of devices deteriorate eventually. Furthermore, in general,the lower the ratio of the area of the wafer 10 to which a highfrequency voltage is applied to the effective ground area, the higherthe V_(dc)/V_(pp) ratio, which provides an index of the applicationefficiency of a high frequency voltage (as shown in FIG. 4, V_(pp) is apeak-to-peak voltage of a high frequency voltage). When the diameter ofthe wafer 10 is increased from 200 mm to 300 mm, the ratio of the areaof the wafer 10 to the effective ground area increases and hence theplasma potential increases, it has become important to take measuresagainst the pollution with metal. In the case of the present invention,the larger the duty ratio becomes, the more the plasma potential can bereduced, providing the advantage that the pollution with metal can beprevented.

Although in each of the above embodiments a description was given of thecase where a high frequency voltage is applied to the wafer 10, there isno restriction to the case so long as where a high frequency voltage isapplied to the interior of the processing chamber. For example, in thecase of an insulating film etching apparatus, by installing a siliconplate in a position opposite to the wafer 10 and applying a highfrequency voltage, excessive fluorine radicals in the plasma generatedby a fluorocarbon gas are removed and the selecting etching ratio of amask is improved. In the case of such an apparatus, the same action andeffect can also be obtained by ensuring that the voltage in the siliconplate obtains a rectangular high frequency voltage waveform. Also, thesame effect is obtained by ensuring that the voltage in both the wafer10 and the silicon plate obtains a rectangular high frequency voltagewaveform, and a greater effect (in particular, the effect of suppressingthe plasma potential) is obtained by adopting the same frequency of thehigh frequency voltage of the two and controlling a phase difference inthe voltage of the two (particularly, a phase difference of about 180degrees). Particularly in the case of an insulating film etchingapparatus, because a high frequency voltage of high output is applied tothe wafer 10, the plasma potential increases and the side wall of theprocessing chamber 1 is sputtered and plasmas are diffused to the lowerpart of the processing chamber 1, posing the problem of occurrence ofcontaminants. However, in the case of this embodiment, the plasmapotential can be suppressed, which is effective in reducing theformation of contaminants, providing the advantage of an improvement inthe operation rate of the apparatus and an increase in yield.

Although the impedance matching network 11 was used in the aboveembodiments, for the sake of simplification, it is also possible toreplace the impedance matching network 11 with a high frequencytransformer or exclude the impedance matching network 11 if the matchingwith the plasma load can be ensured to a certain degree. Also, the sameaction and effect can be obtained, for the sake of simplification, byuse of an arbitrary signal generator and a high frequency poweramplifier, wherein a voltage waveform in which an absolute value of highfrequency voltage increases with time as shown in FIG. 3 is applied tothe wafer chucking electrode 9. Although in the above embodiments adescription was given by using a rectangular wave as an ideal case,almost the same action and effect can be obtained even by using atrapezoidal wave or similar waves having a waveform which is a littledisturbed due to frequency characteristics.

Embodiment 2

The second embodiment of the present invention will be described withreference to FIG. 13. In this figure, the same reference numerals as inFIG. 1 indicate the same parts and hence the descriptions of these partsare omitted. Points of this figure which are different from FIG. 1 willbe described below. The rectangular high frequency power source 13 isconstituted by a DC power source 17 and a switching circuit 18 (achopper circuit). A pulse waveform can be output by repeating the on andoff operation of the DC output from the DC power source at a high speedby use of a switching element. As a result of this, the same action andeffect as in Embodiment 1 can be obtained and the construction of therectangular high frequency power source can be simplified. As theswitching element used in the switching circuit (the chopper circuit)18, it is possible to use a thyristor, a GTO (a gate turn-offthyristor), an IGBT (an insulated gate bipolar transistor), a MOSFET, apower transistor, and so on. Furthermore, by connecting these switchingelements in series and in parallel, it is possible to increase theswitching frequency, withstand voltage and withstand current and thefrequency of a rectangular wave capable of being applied to the wafercan be increased to about several MHz. Also, by controlling the on-offsignal of the switching element, a voltage waveform in which an absolutevalue of high frequency voltage increases with time as shown in FIG. 3is generated. Therefore, the same action and effect as in Embodiment 1are obtained even by applying this high frequency voltage to the waferchucking electrode 9. In this case, the high frequency voltage waveformcontrol circuit (sag correction circuit) 12 can be omitted, and theautomatic control of the switching circuit 18 (the chopper circuit) isperformed by using, for example, a signal from the electrode currentmonitor 15 as a monitored quantity.

Embodiment 3

The third embodiment of the present invention will be described withreference to FIG. 14 to FIG. 19. In this figure, the same referencenumerals as in FIG. 1 indicate the same parts and hence the descriptionsof these parts are omitted. Points of this figure which are differentfrom FIGS. 1 and 2 will be described below. The rectangular highfrequency power source 13 is constituted by a sine wave output powersource 19. A sine wave voltage waveform output from the sine wave outputpower source 19 is clipped by the high frequency voltage waveformcontrol circuit (sag correction circuit) 12, and a voltage waveform inwhich an absolute value of voltage in a clipped portion increases withtime is generated. As a result of this, it becomes possible to apply awaveform close to a rectangular high frequency voltage waveform to thewafer. This enables the same action and effect as in Embodiment 1 to beobtained and the construction of the rectangular high frequency powersource to be simplified.

FIG. 15 (B) shows a waveform in which sag ratio of 0% was achieved in awafer by clipping sine wave voltage waveform. Control was performed sothat the sag ratio becomes 0% at the wafer potential by varying the clipvoltage to −400 V and −200 V for a sine wave voltage waveform of VPP 700V with sag correction. FIG. 15 (A) shows three-dimensionally the resultof the measurement of the ion energy distribution in each wafer voltagewaveform. Although in a sine wave voltage waveform of V_(pp) 700 V theproportions of the quantity of ions at a high energy peak and a lowenergy peak are each about 50%, the quantity of ions at the high energypeak is increased by setting the clip voltage at −400 V and −200 V andthe period of the flat part. In other words, an ion energy distributionclose to a monochromatic one can be obtained. When the peak quantity ofions on the low energy side is denoted by P_(L) and the peak quantity ofions on the high energy side by P_(H), the high energy peak ratio isdefined as follows: $\begin{matrix}{\left\lbrack {{Formula}\quad 3} \right\rbrack{{{High}\quad{energy}\quad{peak}\quad{ratio}\quad(\%)} = {\frac{P_{H}}{P_{L} + P_{H}} \times 100}}} & (3)\end{matrix}$

FIG. 17 shows the V_(pp) dependence of the high energy peak ratio. Thehigh energy peak ratio of an ideal monochromatic ion energy distributionis 100%, whereas the high energy peak ratio is about 50% in aconventional sine wave bias. In the sine wave clip voltage waveform withsag ratio of 0% shown in FIG. 15 (A), the high energy peak ratio can beincreased to about 85%.

The dependence of the ion energy distribution on the sag ratio is shownin FIG. 18 (A). FIG. 18 (B) shows a wafer voltage waveform which wascompensated for in terms of sag and in which the sag ratio was varied atthe wafer potential from 0% to 13%, and FIG. 18 (A) showsthree-dimensionally the result of the measurement of the ion energydistribution at each ratio of the amount of sag. When the sag ratioincreases, the peak quantity of ions on the high energy side P_(H)decreases. FIG. 19 shows the dependence of the high energy peak ratio onthe sag ratio. When the high energy peak ratio is 80% or greater, theratio of the amount of sag must be not more than 10% in order to achievean ion energy distribution close to a monochromatic one.

Although in the above embodiments the frequency of the rectangular highfrequency power source 13 was 400 kHz and 800 kHz, a frequency in therange of 10 kHz to 4 MHz or so is preferred in consideration of thefollow-up action of ions to alternating electric fields, and a frequencyin the range of 100 kHz to 2 MHz or so is preferred in consideration ofthe incidence efficiency of ions on the wafer.

Although in the above embodiments a description was given of the exampleof an etching apparatus based on the use of a magnetic field UHFdischarge, the same action and effect can be obtained also from a dryetching apparatus which utilizes other discharges (a magnetic fieldmicrowave discharge, a capacitive coupled discharge, an inductivelycoupled discharge, a magnetron discharge, a surface wave excitationdischarge, and a transfer coupled discharge). Although in the aboveembodiments a description was given of an etching apparatus, the sameaction and effect can be obtained also from other plasma processingapparatus which perform plasma processing, such as a plasma CVDapparatus, an ashing apparatus and a surface modification apparatus.

1. The plasma processing apparatus wherein the means for applying a highfrequency voltage, which becomes a voltage waveform in which a positiveconstant voltage and a negative constant voltage alternate with eachother at given cycles, is constituted by a DC power source and aswitching circuit (a chopper circuit).
 2. The plasma processingapparatus according to claim 1, wherein the means for applying a highfrequency voltage, which becomes a voltage waveform in which a positiveconstant voltage and a negative constant voltage alternate with eachother at given cycles, is constituted by a DC power source and aswitching circuit (a chopper circuit), which uses as switch elements athyristor, a GTO (a gate turn-off thyristor), an IGBT (an insulated gatebipolar transistor), a MOSFET and a power transistor.